Device for securing a dental attachment to an implant

ABSTRACT

An anchorage unit ( 41, 44 ) fits to a dental implant ( 5 ). A dental attachment ( 31, 32 ) for mounting to the anchorage unit comprises a first attachment part ( 31 ) and a second attachment part ( 32 ). The attachment parts ( 31, 32 ) define an aperture ( 24 ) for accommodating a portion ( 44 ) of the anchorage unit with a boundary wall of the aperture ( 24 ) on each of the attachment parts serving, in use, as a jaw for clamping against the portion of the anchorage unit. The aperture is of greater size than the portion of the anchorage unit to allow adjustment of the position of the attachment with respect to the anchorage unit. In another embodiment, a two-part anchoring assembly defines a pair of jaws for, in use, receiving and clamping against a portion of a dental attachment. The apparatus is particularly relevant when an attachment must be placed on more than one implant simultaneously.

FIELD OF THE INVENTION

The present invention relates to securing a dental attachment, such as adental bridge or other dental prosthesis, to a dental implant which hasbeen implanted in a patient's jaw as well as to methods of constructingand using the dental attachment. The invention is particularly relevantwhen an attachment must be placed on more than one implantsimultaneously.

BACKGROUND TO THE INVENTION

It is known to secure a dental attachment, such a dental bridge or otherdental prosthesis, to implants which have been implanted into apatient's jaw bone. An attachment can be manufactured after the implantis placed in the jaw bone or before the implant is placed in the jawbone.

Where the attachment (e.g. bridge) is manufactured after the implantshave been installed in the patient, an impression is typically taken ofthe mouth to determine the locations of the implants relative to the jawand each other. In such cases, it is possible to plan, with somecertainty, the size and shape of the attachment and the attachment isdesigned to have very limited play with respect to the implants. Somelimited adjustment can be provided by recesses in the attachment and theanchorage elements (also known as abutments) on the upper part of theimplants. When the attachment is fitted to the implant, cement isapplied to the internal surface of the recess of the attachment and theexternal surface of the abutment to overcome any play between theseparts. Cement, or cement-like agents, may pose problems related tohardening. Most cement types harden very rapidly, making it difficultduring the hardening process to achieve exact and permanent positionsfor the bridge. Moreover, cement may be difficult to handle in the mouthof a patient (for example, determining the correct amount of cement touse) and may cause soiling of the restoration site.

Where the attachment is designed and manufactured prior to theinstallment of the implants—for so-called ‘immediate loading’—the amountof play between the attachment and the implant can be considerablylarger. The information about the expected implant positions must comefrom an implant planning system (such as SimPlant™ from Materialise NV,Belgium). The implant planning system allows a clinician to determinethe optimal position of the implants in a computer environment showingdigital information of the patient (for example CT, images). The implantplan can be used to design and manufacture the attachment and means(e.g. surgical templates such as SurgiGuide™, Materialise NV, Belgium)are used to transfer the planning to the patient. The play between theimplants after installation and the attachment depends on themanufacturing tolerances of the bridge and the inaccuracies inherent tothe medical imaging for implant planning and the surgical process oftransferring the planning to the patient. Typically the play will rangefrom 0 to 0.5 mm in the lateral direction (known as the mesio-distal orbucco-lingual direction), 0 to 0.5 mm in the vertical direction (knownas the coronal-apical direction) and 0 to 5° in an angular direction(i.e. rotation about a vertical axis through the implant site). Forexample, a two-stage procedure can be used. The implants are installedand an impression taken of the post-operative situation several weeksafter the surgical intervention. Using impression copings, the exactpositions of the implants in the mouth are transferred to a gypsummodel. Implant replicas embedded in this model allow a dental technicianto manufacture a prostheses that fits exactly on the implants in the jawof the patient. A disadvantage of this approach is that the prosthesiscannot be produced prior to installment of the implants.

There have been various proposals to provide a degree of adjustmentbetween an implant and an attachment. International Patent ApplicationWO 03/061512 describes a dental attachment with a longitudinallyextending recessed wall. An implant has a longitudinally-extendingportion which can fit within the recessed wall of the attachment andwhich can expand to anchor the attachment in a relative longitudinaldisplacement relative to the portion of the implant. The use ofexpandable components has the disadvantage that, in the expanded state,recesses are present between the flanges of the expanded component (forinstance in the radial direction). These recesses are likely locationsfor bacteria to settle, possibly causing infections during later stagesof treatment. Furthermore, using the expandable abutments, the loads aretransferred to the implants by friction. This may cause problems ofloosening of the attachment in case of clenching by the patient.

International Patent Application WO 2005/053564 describes a system toovercome lateral misalignments. An anchorage part of an attachmentcomprises a hole for a retaining screw and the neck of the retainingscrew is smaller than the hole in the anchorage part. InternationalPatent Application WO 92/03984 describes a device for anchoring a dentalattachment to overcome angular deviations in the play between the bridgeand the implants.

Each of the above solutions only permit adjustment of an attachmentrelative to an implant in a single direction (longitudinal, lateral orangular).

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of securing adental attachment, such as a dental bridge or other dental prosthesisand/or to a dental implant which can be, or has been, implanted in apatient's jaw as well as to methods of constructing and using the dentalattachment. The present invention seeks to reduce or overcome at leastone of the problems of the prior art methods and devices.

A first aspect of the present invention provides a dental attachmentassembly for fitting to a dental implant comprising:

-   -   an anchorage unit for fitting to the dental implant; and,    -   a dental attachment for mounting to the anchorage unit, the        dental attachment comprising a first attachment part and a        second attachment part which define an aperture for        accommodating a portion of the anchorage unit, with a boundary        wall of the aperture on each of the attachment parts serving, in        use, as a jaw for clamping against the portion of the anchorage        unit.

The invention is particularly relevant when an attachment must be placedon more than one implant simultaneously. Attachment means any structure(with a regular or irregular cross section, regardless of the materialused) intended to connect at least two implants and used to transferloads (for instance as a result of mastication) to these implants.Clamping a dental attachment to an anchorage unit provides a secureconnection between these parts and avoids the problems of cement andexpandable parts. A further advantage of clamping is that one of theattachment parts can be a functional (i.e. load bearing) part and asecond of the attachment parts can be an aesthetic part. If connectingthe two parts of the attachment is performed by means other than screws(for example, by the dental equivalent of buttons), a common problemreferred to as screw loosening can be avoided. Screw loosening occurswhen the small screw used to attach the prosthesis to the implantsunscrews and the prosthesis thereby sits less stably on the implants.

An advantage of having the part of the anchorage unit protruding throughthe attachment is that the size of the attachment can be reduced, whichis advantageous in the mouth because of the limitations in space and thefunctional relation with antagonists.

Preferably, an interface between the first attachment part and thesecond attachment part is substantially parallel to a longitudinal axisof the attachment (e.g. the attachment is divided into a lowerattachment part just above the patient's gums and an upper attachmentpart.) This considerably eases the fitting of the anchorage units andthe attachment parts and allows the interface between the attachmentparts to be concealed by overlapping the upper attachment part (whichtypically carries artificial dentures) over the lower attachment part.For some embodiments it also allows the upper attachment part to bemanufactured after the lower attachment part has been successfullyfitted to the patient. Thus, if it is found that the lower part does notsuccessfully fit on the set of implants, only the lower attachment partneeds to be modified or replaced, without the need to replace an entireattachment. In general a prosthesis for immediate loading will typicallynot be the final prosthesis. One of the advantages of this embodiment ofthe present invention is that costs are reduced because only one part ofthe prosthesis, rather than the entire prosthesis, needs to bere-manufactured. The lower attachment can be accommodated in a recesslocated on a side of a drilling template facing the treatment site whereimplants are to be fitted. This allows the implants to be fitted throughthe lower attachment part, thereby allowing an improved fit.

Preferably, the aperture is of greater size than the portion of theanchorage unit whereby to allow adjustment of the position of theattachment with respect to the anchorage unit. For example, the aperturecan have a width which is greater than the portion of the anchorage unitwhereby to permit adjustment in at least a lateral direction.

Preferably the anchorage unit comprises first and second anchorageelements which are adapted, in use, to secure at a range of differentlongitudinal displacements with respect to one another whereby toprovide an amount of longitudinal (apico-coronal) adjustment.

Adjustment of the position of the attachment with respect to theanchorage unit in an angular direction can be accommodated by a suitablesize of the aperture in the attachment. Alternatively, a rotatableconnection can be provided between parts of the anchorage unit.

A second aspect of the present invention provides an anchoring assemblyfor securing a dental attachment to a dental implant, the assemblycomprising:

-   -   a first anchorage element for fitting to a head of the dental        implant, and    -   a second anchorage element for fitting to the first anchorage        element, the first and second anchorage elements together        defining a pair of jaws for, in use, receiving and clamping        against a portion of the dental attachment.

It will be understood that both aspects of the invention are solutionsto the problem of securing an attachment to an implant and share thefeature of clamping between an attachment and an anchorage unit.

It is noted that the play between the attachment and the implant may beplanned (for example, where a dental attachment is designed prior toimplant placement in a patient) or may be unplanned (for example, playwhich arises from manufacturing tolerances of the attachment). Theattachments can be manufactured after the implants are placed in the jawbone or before the implants are placed in the jaw bone.

An attachment can be located inside a recess of the template. Theattachment may be only one piece.

The present invention also provides a method of fitting a dentalattachment to at least one dental implant at a treatment sitecomprising: fitting an anchorage unit to the dental implant; and,clamping a first attachment part and a second attachment part around theanchorage unit, wherein the first and second attachment parts define anaperture for accommodating a portion of the anchorage unit, with aboundary wall of the aperture on each of the attachment parts serving asa jaw for clamping against the portion of the anchorage unit.

The method may include the preliminary steps of: locating the firstattachment part inside a recess of a drilling template on a side of thetemplate which will face the treatment site; applying the template tothe treatment site; fitting the implant; removing the template andleaving the first attachment part at the treatment site.

The present invention also provides a method of fitting a dentalattachment to at least one dental implant at a treatment sitecomprising: fitting an anchorage unit to the dental implant; clamping afirst attachment part and a second attachment part around the anchorageunit to achieve a desired fit, wherein the first and second attachmentparts define an aperture for accommodating a portion of the anchorageunit, with a boundary wall of the aperture on each of the attachmentparts serving as a jaw for clamping against the portion of the anchorageunit; replacing the first attachment part and anchorage unit with asingle part which matches the relative positions of the first attachmentpart and anchorage unit which achieved the desired fit.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only,with reference to the accompanying drawings in which:

FIG. 1 shows a first embodiment of the invention, in which a two-partanchorage unit clamps around an attachment;

FIG. 2 shows the use of the apparatus of FIG. 1 to adjust in differentdirections;

FIG. 3 shows a second embodiment of the invention, in which a two-partattachment clamps around an anchorage unit;

FIGS. 4 a-4 c show the use of the apparatus of FIG. 3 to adjust indifferent directions;

FIG. 5 shows a third embodiment of the invention, in which the anchorageunit comprises three parts;

FIG. 6 shows a fourth embodiment of the invention;

FIG. 7 shows a fifth embodiment of the invention;

FIG. 8 shows a surgical template and an implant assembly for fitting toa patient;

FIG. 9 shows the surgical template of FIG. 8 in more detail;

FIG. 10 shows the template after implants have been installed;

FIG. 11 shows one part of an anchorage unit fitted to an implant;

FIG. 12 shows a second part of an anchorage unit fitted to an implant;

FIG. 13 shows an upper attachment part (prosthesis) fitted and thecomponents of the anchorage unit fined to an implant;

FIG. 14 shows sealing between the anchorage unit and attachment;

FIG. 15 shows a comparison of a lower attachment part and anchorage unitused during fitting and a resulting final lower attachment part;

FIG. 16 shows a view of a template according to embodiments of thepresent invention from the gingival side.

FIG. 17 shows temporary fixation of the lower attachment usingosseosynthesis screws according to an embodiment of the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be described with respect to particularembodiments and with reference to certain drawings but the invention isnot limited thereto but only by the claims. The drawings described areonly schematic and are non-limiting. In the drawings, the size of someof the elements may be exaggerated and not drawn on scale forillustrative purposes. Where the term “comprising” is used in thepresent description and claims, it does not exclude other elements orsteps. Furthermore, the terms first, second, third and the like in thedescription and in the claims, are used for distinguishing betweensimilar elements and not necessarily for describing a sequential orchronological order. It is to be understood that the terms so used areinterchangeable under appropriate circumstances and that the embodimentsof the invention described herein are capable of operation in othersequences than described or illustrated herein. FIG. 1 shows a firstembodiment of the invention. A dental implant 5 is embedded with thejawbone of a patient. An attachment (e.g. dental bridge) 1 comprises anaperture 2 in the region where the attachment 1 is required to be fittedto the dental implant 5. The term attachment means any structure (with aregular or irregular cross section, regardless of the material used)intended to connect at least two implants and used to transfer loads(for instance as a result of mastication) to these implants.

The attachment 1 has a flange 3 which projects partially across theaperture 2 to form a stepped edge region. A two-part anchorage unit 10,14 secures the attachment 1 to the implant 5. The anchorage unitcomprises a first, lower, part 10 and a second, upper, part 14. Thelower part 10 has a collar 12 with a central aperture to accommodate theshaft 6 b of a fixing screw. In use, collar 12 of part 10 firmly engageswith the connective part of implant 5 by screw head 6 a. FIG. 1 showspart 10 also sitting on top of implant 5 in addition to being heldagainst abutment 7. It is desirable that part 10 should have a good fitto the implant to minimise the possibility of bacteria settling in theinterface. In this example part 7 is an integral part of the implant 5.However, many types of implant designs may be used with the presentinvention. Part 7 can be an external hexagonal connection) for example.In other implant designs the connection will be internal.

Part 10 has a collar with a radially extending surface 15. Surface 15serves, in use, as a jaw to connect to flange 3 of the attachment 1.Upper part 14 of the anchorage unit fits within part 10 and an interface11 allows parts 10 and 14 to be secured in a desired position withrespect to one another (in direction 21). Interface 11 can comprise ascrew thread, a clip, or another interlock which allows the parts 10, 14to be held tightly in a desired position. The inner diameter of part 14is larger than the outer diameter of screw head 6 a to allow head 6 a topass within. Part 14 has a jaw 16 in the form of a radially extendingsurface. In use, jaws 15, 16 act as a clamp to grasp flange 3 of theattachment 1 to tightly secure the attachment 1 to implant 5.

If required, silicon O-rings or the like (not shown) may be positionedbetween the parts 10, 14 of the anchorage unit and the attachment 1 toensure proper sealing of the aperture 2. The attachment 1 can bemanufactured from any material suitable for dental prosthetics such asmetal, carbon-fibre reinforced plastic, ceramics, etc. It can be eithera final or a temporary dental reconstruction and may (for example, inthe case of a metal attachment with porcelain) or may not (for examplein the case of a metal bar for an overdenture) have a prosthetic finish.

The apparatus shown in FIG. 1 permits adjustment in several differentdirections. Three directions 21, 22, 23 are shown. Direction 21 will becalled the axial or longitudinal direction as it is parallel to thelongitudinal axis 26 of an implant. This is also known as apico-coronaldirection. Direction 22 will be called the lateral or radial directionas it is a shift which is in the radial direction of an implant, andlaterally across the surface of the patient's gums. This direction isalso known as mesio-distal (side-to-side across the mouth) orbucco-lingual (forwards-to-backwards). Direction 23 will be called theangular direction as it represents an angular rotation with respect tothe longitudinal axis 26 of the implant. The terms bucco-lingual,mesiodistal, apico-coronal are well known in the field.

Part 10 of the anchorage unit has a cylindrical shaft 17 which supports,on an inner surface, an interface 11. The outer diameter of the shaft 17(d_(min)) is smaller than the diameter of aperture 2 (d_(apert)) in theattachment 1. The outer diameter (d_(max)) of the jaw 15 is larger thanthe diameter (d_(apert)) of the aperture 2. This provides an amount ofclearance 9 between the shaft 17 and attachment 1 while ensuring thatthe attachment can still be clamped by surface 15. Similarly, the outerdiameter of upper part 14 of the anchorage unit is smaller than thediameter of the aperture 2 in attachment 1 (the diameter being definedby a wall 4) to provide an amount of clearance. The clearance describedabove permits an amount of adjustment, in a lateral direction 22, whenpositioning the attachment 1 with respect to the implant 5. Theclearances described above also permit the attachment 1 to be secured toan implant 5 which has been fitted at an angle which is inclined withrespect to vertical. The upper face of flange 3 is inclined. This allowspart 14 to be inclined without drastically increasing the length ofshaft 17, which supports the interface 11.

FIG. 2 shows an example of an attachment 204 which fits to a set ofthree implants at sites 201, 202, 203. At each of the implant sites, atwo-part anchorage unit connects to the attachment. For the purpose ofillustrating the invention, each of the three anchorage units are shownproviding adjustment in a different one of the three possible adjustmentdirections described above. The attachment 204 is secured by acombination of the clamping actions provided by the three implant sites201, 202, 203. At implant site 203 an anchorage unit prevents theattachment 204 from moving in an upward direction. Movement of theattachment in the downward direction is limited by the anchorage unitsat sites 201, 202.

In FIG. 1 the attachment 1 has a stepped cross-section in the region ofthe aperture 2 to provide a flange 3 having a reduced depth (indirection 21) compared to the normal depth of attachment 1. It is notessential to provide this stepped cross-section, and parts 10, 14 of theanchorage unit can clamp against the upper and lower surfaces of theattachment.

FIG. 3 shows a second embodiment of the invention. This embodiment usesthe same principle of securing an attachment to an implant by clampingas FIG. 1. However, in FIG. 3 a two-part attachment 31, 32 clampsagainst a part 44 of an anchorage unit 41, 44 fitted to the implant 5.As before, a dental implant 5 is embedded with the jawbone of a patient.An attachment (e.g. dental bridge) is formed in two parts: a lowerattachment part 31 and an upper attachment part 32. The two attachmentparts 31, 32 join along an interface 34 which is substantially parallelto the upper surface of patient's jaw and substantially perpendicular tothe longitudinal axis 26 of an implant. The two attachment parts 31, 32are held together by fixing screws 33 or the like (clips for example).The attachment parts define an aperture 24, 25 in the region where theattachment is required to be fitted to the dental implant 5. Theaperture has a central shaft 25 which connects an upper face ofattachment part 32 with a lower face of attachment part 31. The shaft 25is at least as wide as the head 6 a of the fixing screw 6 and serves toallow access to the implant. A part 24 of the aperture, in the region ofinterface 34, has a greater width to define a chamber for receiving aportion of the anchorage unit. In this embodiment chamber 24 is locatedwithin the lower attachment part 31. Chamber 24 accommodates a flangedhead of part 44 of the anchorage unit. The lower attachment part 31 hasa flanged portion 37 which projects partially across the aperture 24 toform a stepped edge region. Flanged portion 37 has an upper surface 35which serves as a first jaw. Upper part 32 has a lower surface 36 whichserves as a second jaw. In use, attachment parts 31, 32 clamp tightlyagainst the head of part 44 of the anchorage unit. Chamber 24 isdesigned so that parts 31, 32 will always seal tightly against oneanother and clamp against the head of part 44. The shape of chamber 24and the head of part 44 is designed to facilitate this. Flange 35 isinclined to allow rotation of part 44. The head part of 44 is curvedsuch that when part 44 is inclined the head can move freely within theaperture while maintaining circular line contact with the upper part 32of the attachment.

Anchorage unit 41, 44 is broadly the same as previously described withrelation to FIG. 1. As previously described, the two-part anchorage unit41, 44 engages with the connection part 7 of the implant 5. Theanchorage unit comprises a first, lower, part 41 and a second, upper,part 44. The lower part 41 has a collar 43 with a central aperture toaccommodate the shaft 6 b of a fixing screw. In use, collar 43 of part41 is firmly engages with the connection part 7 of implant 5 by screwhead 6 a. Upper part 44 of the anchorage unit fits within part 41 and aninterface 42 secures parts 41 and 44 in a desired position with respectto one another in direction 21.

An O-ring (e.g. silicon) or other sealing element 48 fits around part 41of the anchorage unit and provides a seal between part 41 of theanchorage unit 41 and the lower attachment part 31.

The apparatus shown in FIG. 3 permits adjustment in several differentdirections. Firstly, adjustment in the lateral direction 22 will beconsidered. There is a clearance (A) between the outer circumference ofpart 44 and wall 38 of lower attachment part 31. Similarly, there isclearance between the outer diameter of part 41 of the anchorage unitand surface 39 of the lower attachment part 31 (seal 48 is flexible).Lower attachment part 31 can be shifted in a lateral direction 22. Themaximum extent of lateral adjustment is reached when the head of part 44rests against wall 38. FIG. 4 a shows how the apparatus of FIG. 3 can beused to provide adjustment in the lateral direction.

Secondly, adjustment in the longitudinal direction 21 will beconsidered. Parts 41 and 44 can be secured at a desired position alongthe longitudinal axis 26 via interface 42. FIG. 3 shows an adjustment Bin the longitudinal direction and the value of B can either be reduceduntil the head of part 44 rests on part 41, or increased until someminimum overlap of the respective collars of parts 41, 44 is reached. Asattachment 31, 32 is directly secured to part 44, this causes theattachment to be positioned at a desired position (in direction 21)above implant 5. FIG. 4 b shows how the apparatus of FIG. 3 can be usedto provide adjustment in the longitudinal direction.

Thirdly, adjustment in the angular direction 23 will be considered.Parts 31, 41 and 44 are shaped to permit some adjustment in thisdirection. Surface 39 of the lower attachment part 31 has a steppedprofile to accommodate movement of part 41. The inclined upper face ofjaw 35 allows the head of part 44 to slide along the jaw, during afitting operation, to a desired fixing position. The chamber 24 formedby the aperture in lower attachment part 31 and the upper attachmentpart 32 has a depth which is sufficient to accommodate the head of part44 at different angular positions, while still being able to clampagainst the head of part 44. The depth of this chamber 24, and theconvex shape of the head of part 44 allows part 44 to be maneuvered inthe angular direction 23. FIG. 4 c shows how the apparatus of FIG. 3 canbe used to provide adjustment in the angular direction. In FIG. 4 cattachment parts 31, 32 are firmly pressed together. For parts 31, 32 toremain firmly together, jaw 35 has an inclined surface to accommodatethe head of part 44.

Part 41 of the anchorage unit 41 can be fitted to the head of implant 5(e.g. as part of a fixture mount) before the implant is installed in thepatient.

FIG. 5 shows a modification to the embodiment shown in FIG. 3. In thisembodiment the anchorage unit, which connects the implant 5 to theattachment 31, 32, comprises three parts 51, 52, 53. As before,anchorage unit comprises a first part 51 which is mountable to implant 5and a second part 52 which fits within the first part 52 at a selectedoffset in the longitudinal direction. An annular head of part 52 has aconvex lower surface 54. A third part 53 of the anchorage unit has anannular shape and has a concave upper surface 55. Surface 54 of part 52and surface 55 of part 53 have complementary sizes and shapes to allowthe respective parts 52, 53 to slide across one another to a requiredangular position. The interior diameter of part 53 is wider than theoutside diameter of the cylindrical body of part 52 to permit an amountof angular movement (FIG. 5 shows the apparatus turned fullyanti-clockwise so that the cylindrical body of part 52 abuts part 53). Atwo-part attachment 71, 72 clamps around part 53 of the anchorage unit.FIG. 5 shows parts 71 and 72 each having an aperture to provide a cavity75 to accommodate annular part 53. Alternatively, the aperture can existin just the lower attachment part 71. Chamber 75 is wider than the outerdiameter of annular part 53 to permit adjustment in the lateraldirection 22. The apparatus shown in FIG. 5 has an advantage of moresecurely supporting the attachment 71, 72 to the implant 5 in angularorientations. Chamber 75 is the same height as annular part 53 as thereis no need for the chamber 75 to accommodate angular movement of part53, this instead being achieved through the rotatable connection betweenparts 52, 53 of the anchorage unit. There is no need to fix parts 52 and53 together. As soon as an attachment is placed on more than one implantsimultaneously, parts 52 and 53 cannot move because this would requirean angular movement of the attachment, which will be blocked by theanchorage unit(s) on the other implant(s).

Another way to achieve movement in the lateral direction is to modifypart 51 to the way shown in WO2005/053564. In this case, aperture 75 canbe exactly the same size as part 53.

FIGS. 6 and 7 show two further embodiments which are particularlyeffective at securing an attachment to an implant at various angularorientations. In FIG. 6, a shaft 81 is mounted to implant 5. The shaft81 has a ball-shaped head 82. A disc-shaped part 83 has a central hole84 which serves as a socket. The hole 84 is sized to accommodate head 82and to permit a range of angular movement between disc 83 and head 82.

A two-part attachment 86, 87 clamps around disc 83. A cavity 88 toretain part 83 is provided by apertures in one, or both, of attachmentparts 86, 87. This cavity preferably is wider than disc 83 to permit anamount of lateral adjustment. Shaft 81 can be fixed in implant in asingle mounting position but preferably shaft 81 may be positioned at aselected depth within implant 5 by screw fitting or other suitablefixing which permits a range of fixing depths in direction 21.

In FIG. 7, a cylindrical part 101 is mounted to the head of implant 5and secured to the implant by a fixing screw 6 a. A disc-shaped part 103can be fixed at a desired position along part 101 by a screw thread orother suitable fixing on the interface 102 between parts 101, 103. Part103 has an internal diameter which is just larger than the outerdiameter of part 101. Attachment parts 111, 112 together define agenerally crucifix-shaped internal cavity having a central shaft andleft and right-hand chambers 114. Each of the left and right-handchambers 114 narrow in the region where they join the central shaft.These narrower regions define jaws 115 a, 115 b, 116 a, 116 b. In theorientation shown in FIG. 7 jaw 115 a presses against a lower side ofpart 103 and jaw 116 b presses against the upper side of part 103whereby to clamp the part 103. The cavity within attachment parts 111,112 is wider than parts 101, 103 to permit adjustment in the lateral andangular directions.

In each of the embodiments described above the clamping surfaces of theanchorage unit and/or the attachment can be provided with means toincrease the friction between the anchorage unit and the attachment.Such means could, for example, comprise small teeth that bear down on tothe clamped part, granules (grains) interlocking into one anotherrespectively on the clamping and the clamped parts or a material withhigh coefficient of friction (e.g. rubber) applied to the respectivesurfaces.

In each of the embodiments shown in FIGS. 3-7 the upper attachment part32 can be part of the final reconstruction while the lower attachmentpart can be a temporary construction.

FIGS. 8-14 show a sequence of steps of a process for installing implantsin the mouth of a patient and for fitting an attachment to the implants.The apparatus of FIG. 3 is used as an example, although any of theapparatus of the present invention could be used in this method. Priorto the step shown in FIG. 8, a treatment planning process plans theposition of implants in a patient's mouth. This typically involvesmapping the patient's mouth by use of a mould or a computerised scanningprocess. Part of this planning process includes choosing sites toinstall implants. A surgical template 120 is created to help inaccurately transferring the treatment planning to the patient's mouth.The template 120 is shown in more detail in FIG. 9. The surgicaltemplate 120 exactly fits onto the gums 122 of the patient. The template120 has a set of holes 121 which match the positions where implants arerequired to be fitted. Template 120 also holds the lower part 31 of atwo-piece attachment. The template 120 is designed to hold the lowerattachment part 31 in a cavity 124 on the bottom side (i.e. the sidethat engages with the patient) which has exactly the shape as the lowerattachment part 31, with no undercuts so the attachment part can stillbe removed. After production of the template 120 the attachment part cansimply be mounted into position by inserting it in the cavity 124. Assoon as the template 120 is positioned on the patient the attachmentpart 31 can no longer move. Because the implants 5 are now fitted to thepatient by passing them through the lower attachment part 31, there isan increased likelihood that the implants 5 will be correctly placed inpositions which allow immediate attachment.

Prior to placing the surgical template 120 on the patient, a thin layerof an inert filler such as silicon is applied onto the down-facing (i.e.gingival) side of the lower attachment part 31. This silicon layer fillsany gaps between the soft tissue and the template 120 when positioningthe latter on the patient and acts as a spacer between the lowerattachment part 31 and the soft tissue of the patient. Each hole of thetemplate is defined by a guide tube 123 which indicates the correctposition and inclination of the implant. An implant 5 is installedthrough one of the holes 121. Attached to the head of an implant 5 isthe first, lower, part 41 of the anchorage unit. Together, the implantand part 41 are mounted on an implant holder 125, with implant holderscrews 126 keeping the assembly together. The implant holder 125 engageswith part 41 via a tooth-and-groove connection 127 to transfer thetorque applied to the holder 125 to part 41 and implant 5 during implantinstallation. Referring to FIG. 10, the lower attachment part 31 can besecured by screws 130 which are fixed into the bone of the patient,engaging with holes in the lower attachment part 31 which are providedin advance for this purpose. Screws 130 are separate fixings from theimplants. Typically osseosynthesis screws are used which do not presentany added risk of infection.

By fixing the lower attachment part 31, the surgical template 120 isalso fixed. Small shifts of the template 120 during surgery due tohandling of the template inside the mouth can no longer occur. As thesurgical template 120 holds the lower attachment part 31, fixing thelower attachment part 31 also serves to stabilise the template 120 onthe gums 122. Also, fixing the lower attachment part 31 to the boneallows the template 120 to be subsequently removed easily withoutremoving the attachment part 31 itself.

As further explanation, the lower attachment 31 can be placed inside therecess 124 of the template 120 as shown in FIG. 16. To make sure it doesnot fall out during the manipulation of the template before it is seatedon the recipient site in the mouth of the patient, some suitable holdingof filling material 49 may be applied, e.g. silicon. Once the template120, with the attachment 31 slotted into it has been correctlypositioned on the patient some osseosynthesis screws 130 may be appliedthrough the holes in the template 120 that firmly lock the lowerattachment 31 onto the recipient site—see FIG. 17. In this manner notonly the attachment but also the guide are stable. The guide is in factstabilized further because of the interaction with the lower attachment.However because the osseosynthesis screws 130 work directly on theattachment, the template itself is not “screwed down”. Once the implantshave been installed and the implant holders have been removed, the guidecan be removed. The lower attachment 31 however is kept in positionthanks to the screws 130. Further along the intervention, the lowerattachment 31 is anchored by means of the anchorage parts. At that pointthe ossesynthesis screws 130 are removed. The apertures in the lowerattachment 31 through which the ossesynthesis screws 130 were placedthen function as recipient sites for small screws 33 that allow upperand lower attachments to be connected as shown in FIG. 3, for example,although any of the apparatus of the present invention could be used inthis method.

FIG. 11 shows one implant installed in the jaw. The implant holder 125and the template 120 are removed after installation, leaving in placethe lower attachment part 31. The implant holders 125 are removed one ata time, replacing the implant holder screws 126 with fixture screws 6,firmly locking the abutting pieces 41 into position on the implants 5.As can be seen in FIG. 11, there is clearance 131 between the aperturesin the lower attachment part 31 and abutting piece 41. The other screwhole shown in FIGS. 11 and 12 is for receiving a screw (33, FIG. 3)which will keep the upper and lower attachment parts together.

The second, upper, part of each of the anchorage units are fixed ontothe abutting pieces 41. As shown in FIGS. 12 and 13, the second part 44engages in the abutting piece 41 via a screw thread 132 provide on itsouter surface (interface 42, FIG. 3). The second piece 44 is screweddown until its head contacts with the lower attachment part 31, as canbe seen in FIG. 12. Any play between the lower attachment part 31 alongthe axes of the implants relative to what was intended is compensated byscrewing the two pieces 41, 44 of the anchorage units together to agreater or lesser degree. The screws 130 fixing the lower attachmentpart 31 to the jaw bone are then removed. The upper attachment part 32is then placed onto the lower attachment part 31 and fixing screws 33are fitted and tightened to rigidly clamp the attachments parts 31, 32to the anchorage unit. By removing the screws 130 at this stage, changein the position of the lower attachment part is prevented. Deviationsfrom the desired positions are generally small enough not to have therequirement of removing the screw 130 earlier. Optionally, the screw canbe removed earlier (e.g. directly after fitting the first part 41 of theanchorage unit) so that the attachment part 31 can be moved intoposition with respect to the set of implants.

At this point, the attachment 31, 32 has been properly positioned withrespect to the set of implants 5. A final stage removes the attachmentparts 31, 32 and anchorage unit 41, 44 from the implants by unscrewingthe fixture screws 6. As attachment parts 31, 32 and the parts 41, 44 ofthe anchorage unit are all fixed together they can be removed as oneunit. The channel (25, FIG. 3) directly above the fixture screw head 6 aallows access to the screw head 6 a. The silicon which was previouslyapplied between the lower side of attachment part 31 and the gums of thepatient is now removed and sealing rings 48 (FIG. 14) are placed overthe anchorage unit parts to shield the gap between them and the lowerattachment part 31. The attachment 31, 32 and anchorage unit 41, 44 canthen be positioned back onto the implants 5 and fixed again with thefixture screws 6.

In screw-retained prostheses the screws need to be accessible. Afterapplying the aesthetic finish (e.g. porcelain) to the attachment part 32the holes are filled with a component that can—if necessary—be removedeasily.

FIG. 15 shows an alternative final stage. The attachment parts 31, 32and anchoring unit 41, 44 are removed from the set of implants byunscrewing fixture screws 6. The upper attachment part 32 is removedfrom the remainder of the assembly and a final part 150 FIG. 15 isformed which has the shape of the set of parts 31, 41, 44, 48. This new,final, part 150 is secured to upper attachment part 32 and then placedupon the set of implants 5 and secured to the implants 5 by reaffixingscrews 6. This alternative scheme has an advantage of creating a finalpart 150 which lacks any gaps between parts. This can provide a muchbetter sealing against the gum. The shape of the final part 150 isdetermined by transferring the final implant positions after healing tothe design environment, e.g. either directly via scanning or indirectlyby first transferring them to a working model e.g. a gypsum cast, whichis scanned afterwards. Given the known position of the implants and theknown dimensions of the upper part of the attachment the design can beperformed accurately.

1-24. (canceled)
 25. A dental attachment assembly mountable to ananchorage unit of a dental implant, the attachment assembly comprising:a first attachment part and a second attachment part which define anaperture for accommodating a portion of the anchorage unit, with aboundary wall of the aperture on each of the attachment parts serving,in use, as a jaw clampable against the portion of the anchorage unit,wherein the aperture has a greater size than the portion of theanchorage unit, to thereby allow adjustment of the position of theattachment with respect to the anchorage unit, a removable dentalimplant drilling template for use at a treatment site where the dentalimplant is to be fitted, wherein the template comprises a hole whichdefines a position for the implant and a recess, located on a side ofthe template facing the treatment site, for accommodating one of saidattachment parts of said dental attachment assembly.
 26. A dentalattachment assembly comprising a dental implant, an anchorage unit forfitting to the dental implant, and a dental attachment assemblyaccording to claim 25 for mounting to the anchorage unit.
 27. A dentalattachment assembly according to claim 26, wherein the aperture has awidth which is greater than the portion of the anchorage unit whereby topermit adjustment in at least a lateral direction.
 28. A dentalattachment assembly according to claim 26, wherein at least a radiallyoutermost region of the aperture has a height which is greater than theportion of the anchorage unit to thereby permit adjustment in an angulardirection.
 29. A dental attachment assembly according to claim 26,wherein the aperture has a central shaft connecting an exterior face ofthe attachment with the aperture for permitting access to the implant.30. A dental attachment assembly according to claim 26, wherein theanchorage unit has a radially extending flange against which, in use,the attachment parts can clamp.
 31. A dental attachment assemblyaccording to claim 26, further comprising at least one fixing elementarranged to secure the first and second attachment parts together.
 32. Adental attachment assembly according to claim 26, wherein the anchorageunit comprises a first anchorage element adapted to fit to the dentalimplant and a second anchorage element adapted to fit to the firstanchorage element, the first and second anchorage elements beingadapted, in use, to be secured with respect to one another within arange of different longitudinal displacements.
 33. A dental attachmentassembly according to claim 32, wherein the second anchorage elementcomprises a radially extending flange against which, in use, the firstand second attachment parts can clamp.
 34. A dental attachment assemblyaccording to claim 32, wherein the second anchorage element is adaptedto be fit within the first anchorage element.
 35. A dental attachmentassembly according to claim 32, wherein the second anchorage element isadapted to be fit around the outer surface of the first anchorageelement.
 36. A dental attachment assembly according to claim 32, whereinthe first anchorage element is connectable to the second anchorageelement by a rotatable connection.
 37. A dental attachment assemblyaccording to claim 36, wherein the first anchorage element comprises ashaft having a head and the second anchorage element comprises a socketfor receiving the head and permitting, in use, rotation of the secondanchorage element with respect to the first anchorage element.
 38. Adental attachment assembly according to claim 32, wherein the secondanchorage unit comprises a head with a radially extending flange.
 39. Adental attachment assembly according to claim 38, wherein the head has aconvex upper surface.
 40. A dental attachment assembly according toclaim 32, further comprising a third anchorage element to which, in use,the attachment can clamp, the second anchorage element being rotatable,in use, with respect to the third anchorage element.
 41. A dentalattachment assembly according to claim 26, wherein the third anchorageelement is an annular element having a concave upper surface and thesecond anchorage element has a head with a convex lower surface, thehead of the second anchorage element fitting within the third anchorageelement.
 42. A dental attachment assembly according to claim 26, whereinthe anchorage unit comprises a channel for receiving a fixing elementfor engaging with a connection part of the implant.
 43. A dentalattachment assembly according to claim 26, further comprising a seal forfitting around the anchorage unit and for sealing between the anchorageunit and one of the attachment parts.
 44. A dental attachment assemblyaccording to claim 26, wherein an interface between the first attachmentpart and the second attachment part is substantially parallel to alongitudinal axis of the attachment.
 45. A dental attachment assemblyaccording to claim 25, wherein the hole has a diameter sufficient toaccommodate the implant and an anchorage element for fitting to animplant.
 46. A method of fitting a dental attachment to a dental implantat a treatment site comprising: fitting an anchorage unit to the dentalimplant; arranging a first attachment part and a second attachment partof said dental attachment around the anchorage unit, wherein the firstand second attachment parts define an aperture for accommodating aportion of the anchorage unit, with a boundary wall of the aperture oneach of the attachment parts serving as a jaw for clamping against theportion of the anchorage unit; adjusting the position of the dentalattachment relative to the anchorage unit, said adjustment enabled bythe aperture having a greater size than the portion of the anchorageunit with the jaws clamped against said portion; and clamping the firstand second parts around the anchorage unit to fix the position of thedental attachment and the anchorage unit relative to one another.
 47. Amethod of fitting a dental attachment according to claim 46, furthercomprising the step of replacing the first attachment part and anchorageunit with a single part which matches the relative positions of saidfirst attachment part and said anchorage unit which achieved the desiredfit.
 48. A method according to claim 46, further fitting a removabledental implant drilling template for use at a treatment site where thedental implant is to be fitted, wherein the template comprises a holewhich defines a position for the implant, and a recess, located on aside of the template facing the treatment site, for accommodating one ofthe attachment parts of said dental attachment assembly.